1. Field of the Invention
The invention is directed to a registration method for navigation-guided medical interventions, of the type wherein a coordinate transformation between a coordinate system of a position acquisition system and a coordinate system of a measurement volume of a X-ray device is determined, and is employed for the navigation.
2. Description of the Prior Art
Navigation is being increasingly used for supporting medical interventions, meaning that the guidance of a medical instrument relative to a patient or relative to a tissue region of the patient undergoing treatment that is supported by means of optical image information. In image of the instrument is mixed into a 2D or 3D image of the patient acquired with an X-ray device. In this way, an operator can guide an instrument that has at least partly penetrated into the patient and whose tip, for example, is no longer directly visible due to the penetration into body tissue. This instrument is guided relative to the tissue region under treatment on the basis of the image information without running the risk of unintentionally injuring the patient.
In order to enable such a navigation-guided intervention, i.e. in order to be able to mix an image of the instrument into image information of a patient with an accurate position and orientation, it is necessary to produce a mathematical relationship in the form of a coordinate transformation between a coordinate system of the image information of the patient, or a coordinate system of the reconstructed volume of the patient, and a coordinate system with reference to which the positions of the instrument to be navigated are indicated. To this end, artificial marks sometimes are arranged at the patient or anatomical marks are defined, for example prominent bone structures. The anatomical or artificial marks must be clearly visible in the image information of the patient acquired with the X-ray device and must be easily reachable at the patient. The artificial marks are secured, for example, to the skin surface of the patient in order to undertake a registration, which is understood to mean the determination of the spatial transformation rule between the coordinate system in which the positions of the instrument to be navigated are defined and the coordinate system of the image information or of the reconstructed volume, of the patient. The marks usually must be approached with the instrument individually and in the correct sequence in order to be able to determine the coordinate transformation between the two coordinate systems. In the case of extremely precise medical interventions, the marks are rigidly secured to the body of the life form. Examples are the attachment of a stereotactic frame to the head of a patient or the attachment of marks in bones or at the spinal column of a patient. The attachment of the marks may ensue in a separate operation, since the marks must already be attached before a preoperative imaging that is frequently employed for the navigation.
The attachment and registration of the marks, accordingly, is a relatively unpleasant procedure for a patient and also is relatively time-consuming for an operator in preparation for a navigation-guided intervention.